In the short time involved in the birth of a foal, the baby undergoes tremendous physical changes. The foal leaves the protected environment of the uterus where everything is provided and enters a world of light, cold and noise. In her new environment she must change her circulation, breathe air and seek out her own nutrition.

The lungs of the foal undergo the most dramatic transformation at birth. Previously bathed in fluid with no airspaces, and possessing a limited blood supply, the lungs suddenly transform into the oxygen-absorbing organ of the body through which the entire blood volume must flow several thousands of times each day. Several events must come together for this to occur.

During parturition (birth), the foal's chest is compressed as she passes through the pelvic canal of the dam. This mechanical action helps express fluid from the lungs.

The placental blood flow decreases, and the drop in oxygen stimulates the foal to gasp for air. These deep breaths generate a vacuum that sucks air into the lower airways and air sacs for the first time. During the foal's first few breaths, the lungs expand, encouraging fluid to move from the air sacs in the lungs to the pulmonary blood vessels, leaving room for more air than fluid to fill the lungs in subsequent breaths.

While these changes are occurring in the lungs, blood flow is redirected to the blood vessels in the lungs. Before the foal is born, most of the blood flow bypasses the lungs through a detour between the aorta and the main pulmonary artery, called the ductus arteriosus. But the heart has been remodeled so that it can deliver all the blood to the lungs after birth. The ventricular septum, the wall between the left and right side of the heart, was completed by the 38th day of gestation and the foramen ovale, a connection between the left and right atria, should close a few hours after birth.

At birth the initial lung expansion causes a drop in pulmonary blood pressure, allowing the blood to flow from the pulmonary arteries through the capillaries of the lung. Complete closure of the ductus arteriosus should occur by 72 hours after birth. Until that time it is normal to hear a soft heart murmur in the newborn foal.

All of these steps are important for the development of a healthy newborn foal. And they generally take place in the first moments after birth. Problems can develop anywhere along this path, although most foals do this very well. Nevertheless, some need our help.